and \(R\)  is an \(n \times \ell \)  matrix that samples \(\ell \)  coordinates from \(n\)  uniformly at random [1]}. When \(\Omega \)  is a SRFT matrix, we can calculate the matrix multiplication \(Y=A \Omega \)  using \(\mathrm {O}(m n \log (\ell ))\)  flops by applying a subsampled FFT [2]}.
